Tin-Carboxylate MOFs for Sugar Transformation into Methyl Lactate

Article abstract of DOI:10.1002/ejic.201900310

With the purpose of improving the production of methyl lactate (ML) from sugars (glucose and sucrose), a new metal-organic framework (MOF) denoted as UZAR-S10, containing Sn ions and ligand 2-aminobenzene-1,4-dicarboxylate was synthesized. The SEM and PXRD characterization revealed that UZAR-S10 was highly crystalline. The empirical formula of UZAR-S10 is [(NH₂-BDC)Sn]·(NH₂-BDC)_0.5, i.e., per Sn atom, with one structural ligand molecule and half ligand molecule trapped in the MOF structure. The removal of the trapped ligand by either solvent extraction or thermal treatment damaged the structure of UZAR-S10, not enabling its activation. The performance of UZAR-S10 in the production of ML was compared to those achieved with different types of carboxylate MOFs, especially with that of Sn partially substituted Ti tetracarboxylate MOF denoted MIP-177-LT (MIP-177-LT(Ti/Sn)). The highest ML yields achieved from sucrose were 29.5 % and 42.0 % for UZAR-S10 and MIP-177-LT(Ti/Sn), respectively. For comparison, other carboxylate type MOFs (MIL-53(Al), NH2-MIL-53(Al), UiO-66, MIL-101(Cr) and HKUST-1) were tested at the same conditions with worse performance than the two Tin-containing MOFs.

Full text of DOI:10.1002/ejic.201900310

A Journal of
Accepted Article
Title: Tin-carboxylate MOFs for sugar transformation into methyl lactate
Authors: Beatriz Murillo, Beatriz Zornoza, Oscar de la Iglesia, Sujing
Wang, Christian Serre, Carlos Téllez, and Joaquin Coronas
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201900310
Link to VoR: http://dx.doi.org/10.1002/ejic.201900310

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
Tin-carboxylate MOFs for sugar transformation into methyl
lactate
Beatriz Murillo,1 Beatriz Zornoza,1,2 Oscar de la Iglesia,1,3 Sujing Wang,4 Christian
Serre,3 Carlos Téllez,1 Joaquín Coronas1,*
1Chemical and Environmental Engineering Department, Instituto de Nanociencia de
Aragón (INA) and Instituto de Ciencia de Materiales de Aragón (ICMA), Universidad de
Zaragoza-CSIC, 50018 Zaragoza, Spain.
2Department of Energy and Environment, Instituto de Carboquímica-ICB-CSIC, Miguel
Luesma Castán 4, 50018 Zaragoza, Spain
3Centro Universitario de la Defensa Zaragoza, Academia General Militar, 50090
Zaragoza, Spain.
4Institut des Matériaux Poreux de Paris, FRE 2000 CNRS, Ecole Normale Supérieure,
Ecole Supérieure de Physique et de Chimie Industrielles de Paris, PSL University
Paris, 75005, France.
*Corresponding author: Joaquín Coronas. Universidad de Zaragoza. c/ Mariano Esquillor
s/n. 50018 Zaragoza. Spain. Phone: 34 976 762471. Fax: 34 976 761879. e-mail:
coronas@unizar.es
Dr. Beatriz Murillo
Dr. Beatriz Zornoza
Dr. Oscar de la Iglesia
Dr. Sujing Wang
1
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
Prof. Dr. Christian Serre
Prof. Dr. Carlos Téllez
Prof. Dr. Joaquín Coronas
2
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
Abstract
With the purpose of improving the production of methyl lactate (ML) from sugars
(glucose and sucrose), a new metal-organic framework (MOF) denoted UZAR-S10,
containing Sn ions and ligand 2-aminobenzene-1,4-dicarboxylate was synthesized. The
SEM and PXRD characterization revealed that UZAR-S10 was highly crystalline. The
empirical formula of UZAR-S10 is [(NH2-BDC)Sn]·(NH2-BDC)0.5, i.e., per Sn atom,
with one structural ligand molecule and half ligand molecule trapped in the MOF
structure. The removal of the trapped ligand by either solvent extraction or thermal
treatment damaged the structure of UZAR-S10, making not possible its activation. The
performance of UZAR-S10 in the production of ML was compared to those achieved with
different types of carboxylate MOFs, especially with that of Sn partially substituted Ti
tetracarboxylate MOF denoted MIP-177-LT (MIP-177-LT(Ti/Sn)). The highest ML
yields achieved from sucrose were 29.5% and 42.0% for UZAR-S10 and MIP-177-
LT(Ti/Sn), respectively.
Keywords
Biomass, MOF catalysis, Metal-organic framework, Sugar conversion, Lactic acid
3
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
1.
Introduction
Biomass, storing energy from the Sun, has been always present along human being
history. First, as the primary heating source through burning wood; nowadays evoking
the challenge to build a more sustainable world by using biomass to obtain a large variety
of chemical substances. In this context, one of the platform molecules produced from
biomass is lactic acid.[1] This molecule is the most important hydroxycarboxylic acid due
to its wide range of applications in the food, cosmetics, pharmaceutical and chemical
industries.[2] Above all, the main use of this compound is in the polymer market, since
lactic acid is the precursor for biocompatible and biodegradable polymer polylactic acid
(PLA) that is a thermoplastic aliphatic polyester.[3] PLA is used to make commercial
products related to packaging, agriculture, transportation, electronics and houseware,
among others.[4]
Industrially, ca. 90 % of lactic acid is produced by the fermentation of aqueous
glucose.[1] However, this process has some drawbacks such as a long reaction time, high
energy consumption and large amount of waste produced in the needed neutralization and
purification steps.[5] As an alternative to lactic acid production, several industrial routes,
first based on homogeneous catalysis, were proposed from petrochemical resources, such
as acetaldehyde.[6] Moreover, research studies have reported the use of homogeneous
catalysts in the production of lactic acid.[7, 8] For instance, Zhou et al.[7] developed a
method for the conversion of carbohydrates into methyl lactate using SnCl4 as catalyst.
These authors used NaOH to neutralize the protons generated in the methanolysis of
SnCl4, increasing the yield to methyl lactate. However, the used catalysts are toxic and
corrosive and their recovery is difficult, so this homogeneous catalysis route is not an
attractive alternative.
4
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
Focusing on heterogeneous catalysis, where the catalysts could be recovered and
reused with low cost, several solid catalysts have been applied for the conversion of
sugars to lactic acid and derivatives. Different zeolites and ordered mesoporous silicas
(OMSs) were used for this purpose with good results: BEA-type zeolite,[9-11] MFI-type
zeolite,[12] FAU-type zeolite,[13] and OMSs Sn-MCM-41[12, 14, 15] and SBA-15.[12] In
addition, other kinds of solids were applied in this reaction, such as tin-exchanged
montmorillonite clay,[16] supported noble metal catalysts,[17] alumina supported KOH [18]
and carbon-silica composite.[19]
Recently, we tested ZIFs (zeolitic imidazolate frameworks) ZIF-8 and ZIF-67 for
the conversion of sugars (glucose, fructose and sucrose) into methyl lactate.[20] These two
materials belong to a subclass of MOFs (metal organic frameworks) based on 2-
methylimidazolate linker and Zn and Co metals. In fact, there is a great interest in the use
of MOF catalysts in the biorefinery field, and MOFs have been reviewed as catalytic
materials in biomass upgrading to produce value-added fine chemicals.[21] In particular,
ZIF-8 was found to be the most efficient MOF for the conversion of sucrose into methyl
lactate with a yield of 42%.[20] From these previous results and from the fact that Sn-Beta
was the best performing zeolite in the pioneering related work by Holm et al.,[9] we
hypothesized that a possible tin-containing MOF would be able to produce a good
performance in the sugar transformation to methyl lactate. For this purpose, we
investigated the synthesis of carboxylate type MOFs based on metal tin. Thus a new MOF
(from now UZAR-S10) has been discovered based on the combination of tin and 2-
aminobenzene-1,4-dicarboxylic acid. To the best of our knowledge, this is the first time
that this combination has been used to produce a MOF, even though Sn has been
previously coordinated to create MOF type solids with phosphonates,[22] several other
dicarboxylates[23] and porphyrin.[24] In addition, we studied the behavior of the mixed
5
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
metal(IV) tetracarboxylate MOF denoted MIP-177-LT(Ti/Sn), obtained through direct
synthesis by substituting Sn4+ ions into the Ti12 cluster SBU of MIP-177-LT,[25] in the
mentioned reaction.
2.
Results and discussion
2.1. Characterization of UZAR-S10
Fig. 1 shows the PXRD patterns corresponding to several UZAR-S10 samples
obtained at different synthesis durations from 1 h to 48 h. Even if no significant change
of crystallinity was found as a function of synthesis time, due to the fact that 1 h synthesis
showed some PXRD peak intensities lower than those seem at higher times, 5 h was
chosen as the typical synthesis time to obtain powders for characterization and catalysis
application. For comparison, the PXRD pattern of NH2-MIL-53(Al), based on the MIL-
53 topology,[26] is shown. There is no matching between UZAR-S10 and NH2-MIL-
53(Al) patterns, and as far as we know UZAR-S10 is a new phase not previously reported.
However, in spite of the high crystallinity of UZAR-S10, all the attempts carried out until
the moment to solve its structure were unsuccessful. The SEM images of UZAR-S1
obtained at 5 h (Fig. 2) depict also high crystallinity in agreement with the previous PXRD
results. Sheet particles of 3-5 m with ca. 300 nm thicknesses were obtained. The change
of the synthesis time between 1 and 48 h did not produce significant changes in
morphology (Fig. S1).
6
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
UZAR-S10 (48 h)
UZAR-S10 (24 h)
UZAR-S10 (1 h)
UZAR-S10 (5 h)
NH2-MIL-53(Al) (5 h)
5
10 15 20 25 30 35 40
2[º]
Figure 1. PXRD patterns of UZAR-S10 synthesized at 150 ºC for 1-48 h; comparison
with NH2-MIL-53(Al) synthesized at 150 ºC for 5 h.
Figure 2. SEM images of UZAR-S10 synthesized at 150 ºC for 5 h at two different
magnifications.
The elemental analysis carried out on UZAR-S10 revealed wt% concentrations of
37.1 2.4 and 5.8 for C, H and N, respectively. This is in agreement with the atomic
composition of the ligand NH2-H2BDC, probing that its nature was not modified upon the
solvothermal synthesis of the material. As shown in Fig. 3, there is a first loss of weight
(22%) until 330 ºC that is attributed to organic linker molecules trapped in the eventual
7
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
porosity of the MOF. Between 330 and 550 ºC, the loss of weight (44%) is due to
coordinated organic linker. Finally, the remain after 550 ºC (34%) corresponds to SnO2.
This information and the previous statement about the preservation of the linker was used
to estimate the empirical formula of UZAR-S10 as follows: [(NH2-BDC)Sn]·(NH2-
BDC)0.5, i.e. C24H14O12N3Sn2, with one structural linker molecule and half linker
molecule trapped in the MOF structure per Sn atom.
100
90
80
70
60
50
UZAR-S10
DMF
DMF-MeOH
40
MeOH
30
20
100 200 300 400 500 600 700 800
Temperature [ºC]
Figure 3. TGA curves in air of UZAR-S10 synthesized at 150 ºC for 5 h upon treatment
with different solvents.
A problematic issue regards the activation of UZAR-S10. Neither the immersion in
methanol at 70 ºC for 15 h or in DMF at 150 ºC for 15 h nor that in DMF (150 ºC for 15
h) followed by methanol at 70 ºC for 15 h produced the desired activation, giving rise to
materials with respective BET specific surface areas of 6, 23 and 39 m2/g (see the
corresponding N2 isotherms in Fig. S2). As shown in Fig. 3, these immersions,
particularly when carried out in DMF, reduced somehow the 330 ºC step of loss of weight
while increased that assigned to SnO2, in parallel producing a clear decrease in
crystallinity (Fig. S3). In other words, UZAR-S10 seems to be stable in methanol but not
8
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
in DMF and the loss of part of the half molecule of ligand trapped, see the above discussed
empirical formula, triggered the degradation of the material. To gain insight into the MOF
thermal stability and possible thermal activation, UZAR-S10 was submitted to
thermodifractometry under vacuum up to 300 ºC, conditions that clearly deteriorated the
crystalline structure (Fig. 4). Nevertheless, the structure was stable at 275 ºC. This was
corroborated by the PXRD patterns obtained at room temperature upon heating at
increasing temperatures (200, 250, 275, 300, 325 and 400 ºC) for 8 h, as shown in Fig.
S4a. Interestingly, as the treatment temperature increased, the ca. 330 ºC step of loss of
weight was reduced to the point that at 300 ºC when the PXRD was clearly damaged it
almost disappeared (Fig. S4b).
300 ºC
25 ºC
150 ºC
275 ºC
200 ºC
100 ºC
25 ºC
UZAR-S10
5
10 15 20 25 30 35 40
2 [º]
Figure 4. Thermodiffractometry carried out under vacuum maintaining the sample at
each condition for 10 min, starting at 25 ºC (bottom) and finishing at 300 ºC (top); after
275 ºC the temperature was decreased to 150 and 25 ºC and then increased to 300 ºC.
UZAR-S10 obtained at 150 ºC for 5 h.
2.2. Catalytic tests
9
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
UZAR-S10 was first tested in the transformation of glucose into methyl lactate
(ML) in a methanol medium. The results of the glucose conversion of this material are
summarized in Table 1 and compared with the blank experiment (ML yield 1.4%) and
those of other related carboxylate type MOFs: MIL-53(Al), NH2-MIL-53(Al), Zr
containing UiO-66, Cu containing HKUST-1 and MIL-101(Cr). UZAR-S10 reached the
highest ML yield (10.2%) and a similar total yield (i.e. including pyruvaldehyde dimethyl
acetal (PADA), 1,1,2,2-tetramethoxypropane (TMP) and other non-identified products
(n.i.p.)) to UiO-66 (15.1-15.5%). Note that the sugar conversion itself was always ca.
100% in presence of catalyst;[15,20] this is the reason because it was not systematically
estimated (since such value does not contribute to the discussion). In any event, these
values are below the ML (19.8%) and total (22.7%) yields achieved by ZIF-8 in the same
conditions.[20] The poor performance of UiO-66 can be due to the presence of metal Zr,
already demonstrated to be inferior to Sn when studied for sugar conversion in zeolite
beta.[9] UZAR-S10, even having the desired metal for this type of reactions,[9, 10, 15] was
not as efficient as expected due probably to the impossibility of activating its porosity, as
shown above. In addition, it has been reported a higher Lewis acidity for Zn containing
porous solids than for those with Sn in their composition,[27,28] what would favor ZIF-8
over UZAR-S10 for the current studied reactions in this work.
Table 1. Catalytic results obtained for sugar conversion with different catalysts using
glucose (160 ºC for 20 h, 160 mg of catalyst and 225 mg of glucose). Methyl lactate (ML),
pyruvaldehyde dimethyl acetal (PADA), 1,1,2,2-tetramethoxypropane (TMP) and non-
identified products (n.i.p.).
10
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
Yield (%)
PADA TMP
Total
Sugar
Run Catalyst
yield (%)
conv. (%)
ML
n.i.p.
1
2
3
4
5
6
7
8
Blank[20] a
ZIF-8[20]
1.4±0.9
19.8±2.6
0.9±0.2
1.9±0.2
9.7±3.1
0.9±0.3
0.8±0.3
10.2±2.3
2.5±1.4
0.8±0.1
1.3±0.2
2.3±0.3
1.4±0.7
0.1±0.04 4.3±1.3
0.1±0.03 2.0±1.5
0.2±0.07 3.3±0.2
0.3±0.09 5.1±0.9
0.4±0.02 4.0±1.8
8.3
22.7
5.7
88.6
98.1
MIL-53(Al)
NH2-MIL-53(Al)
UiO-66
-
-
-
-
-
-
9.6
15.5
4.1
MIL-101(Cr)
HKUST-1
UZAR-S10
MIP-177-
0.7±0.02 0.1±0.05 2.4±0.2
1.3±0.5
1.3±0.6
2.2±0.2
4.7±0.4
9.0
0.5±0.06 3.1±1.2
0.7±0.02 3.1±0.1
15.1
9
21.8±1.4
2.4±0.4
28.0
>99.7
LT(Ti/Sn)
a Reaction time of 24 h.
It has been reported that the thermostability and hydrolytic resistance of the
disaccharide and the slow release of hexoses from sucrose in solution prevents unwanted
side reactions as compared to the more reactive glucose and fructose.[29] This explains
why sucrose usually gives rise to higher methyl lactate yields than glucose.[9, 20] In
consequence, UZAR-S10 was tested for the sucrose conversion to methyl lactate. Fig. 5
shows ML yields as a function of reaction time using both glucose and sucrose sugars.
Maximum ML yields of 10.2±2.3% and 28.0±4.4% were achieved from glucose and
sucrose at 20 and 24 h, respectively, with some improvement at 48 h (29.5%). It is worth
mentioning that these two sets of reaction conditions did not alter the crystallinity of
UZAR-S10 (Fig. S5) in terms of 2·theta values. However, clear decreases of intensities
can be observed in Fig. S5 for peaks at 17.3º, 17.9º, 24.1º and 29.0º 2·theta values. These
11
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
decreases can be associated with the reduction of the TGA loss of weight at ca. 330 ºC
(Fig. S6), in line with the previous discussion where a direct relation was established
between this weight loss step and structure damage in terms of PXRD. The solid treated
with sucrose was washed with methanol under reflux for 15 h and subsequently dried
overnight at 200 ºC. Then, it gave rise to a BET specific surface area of only 32 m2/g, in
agreement with the small area values above discussed and confirming that the decrease
in the 330 ºC TGA step has to be related to loss of crystallinity and not to the activation
of the MOF porosity.
40
35
sucrose
30
25
20
glucose
15
10
5
0
0
10
20
30
40
50
Time [h]
Figure 5. Yield of methyl lactate (ML) obtained with UZAR-S10 using glucose and
sucrose. Error bars derived from 4 different experiments at the same conditions (160 ºC,
160 mg of catalyst and 225 mg of sugar).
MIP-177-LT (MIP stands for Materials from Institute of porous materials from
Paris), a lately reported porous and robust Ti-MOF comprising a Ti12O15 cluster and a
tetracarboxylate ligand delimiting a 1.1 nm channel type porosity, can be modified by
12
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
replacing Ti atoms in the SBU by other metals.[25] The successful introduction of Sn into
the Ti oxide matrix has been demonstrated through a combination of advanced
characterization techniques (see SI for more information). This has been done to obtain
MIP-177-LT (Ti/Sn), a MOF that now includes in its structure a main group metal (Sn)
useful for the sugar transformation reaction studied here. The results in the preliminary
glucose transformation were the best among all the catalysts tested (see Table 1) with a
ML yield of 21.8%. In consequence, the MOF was tested with sucrose as substrate as
usually gives higher ML yields than glucose.
As shown in Fig. 6 and Table S1, fresh MIP-177-LT(Ti/Sn) achieved a ML yield
of 39.4% (cycle 1), which is above those obtained with UZAR-S10 (28.0%, see Fig. 5)
or with 131 mg of TiCl4 and 21.5 mg of SnCl2·2H2O (26.8%, see Table S1), that
corresponds to the same respective amounts of metals present in MIP-177-LT(Ti/Sn),
under the same conditions (160 ºC for 20 h, 160 mg of catalyst and 225 mg of sugar). The
better performance of MIP-177-LT(Ti/Sn) compared to that of UZAR-S10 can be due to
the more accessible porosity of MIP-177-LT(Ti/Sn). This exhibits BET specific surface
area and pore volume values (see Table 2) of ca. 470 m2/g and 0.42 cm3/g, respectively,
in contrast to UZAR-S10 with no relevant textural properties as shown above. In fact, it
has been reported a BET area of ca. 700 m2/g for the only Ti-containing MOF MIP-
177.[25] The discrepancy between MIP-177-LT(Ti) and MIP-177-LT(Ti/Sn) BET area
values could be due partially to the heavier atomic weight of Sn compared to Ti, since
same total porous volume or surface area values would produce lower specific values for
similar porous structures prepared with weightier components. In any event, the catalytic
activity of these solids is related to the presence of Lewis acid sites, active for the
carbohydrate transformation to ML as proposed for different catalysts, such as Sn salts,[8]
Sn-zeolites,[11] Sn-MCM-41[15] and Zr-SBA-15,[30] In the case of MOFs, these Lewis acid
13
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
sites would come from the presence of metals (e.g. Sn) bearing such sites[31] without
discarding Brønsted acidity[32] generated by the grafting of water or methanol molecules
to unsaturated metal sites.[33]
The catalyst was submitted to five successive reaction cycles at the same conditions
(Fig. 6 and Table S1). After the first cycle the catalyst showed an increase in performance
and the second cycle gave rise to a ML yield of 42.0%. This could be explained by an
extra activation of the MOF during the sugar transformation in the methanol medium. In
agreement with this, some stabilization was reached after the third cycle with a ML yield
of 30.2%, similar to those achieved after the fourth (30.2%) and last fifth (33.4%) cycle.
After four sucrose conversion cycles in the same operation conditions, ZIF-8 showed a
ML yield of 27.2%.[20] Table 2 shows the BET specific surface area and pore volume
values as a function of reaction cycle, obtained from the N2 adsorption isotherms in Fig.
S7. The BET area decreased to 85-112 m2/g after any of the reaction cycles in line with
the adsorption of some of the species involved in the reaction.[20] ZIF-8 showed a decrease
in the BET area from 1390 to 760 m2/g after the fourth reaction cycle with sucrose.[20]
The porosity of MIP-177-LT presents large channels with free diameter of 1.1 nm,[25]
more inclined to fouling with reaction species, due to facilitated access, than the 0.34 nm
pores of ZIF-8,[34] even if it is true that ZIF-8 presents the phenomenon of gate opening[35]
and can allow the hosting of bulkier molecules such as caffeine.[36] Run cycle 1b in Table
S1, that corresponds to a run in which, with the used catalyst from cycle 1, no sugar was
added to the reactor, demonstrated that some reaction species were retained by the catalyst
during the reaction. In fact, the catalyst was “activated” during this run and the BET
specific surface area increased up to 250 m2/g. Table 2 shows also the Ti and Sn
compositions of MIP-177-LT(Ti/Sn) as determined by XRF. Ti content was stabilized or
slightly diminished, while some loss of Sn was detected. This could contribute to the
14
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
lower catalytic activity in cycles 3-5 as compared to the fresh catalyst (cycle 1). In any
event, the crystallinity of the catalyst (see Fig. S8) was not altered upon the reaction cycles
carried out, and after five cycles the XRD pattern obtained resembled well that
corresponding to the fresh catalyst.
50
40
30
20
10
0
cycle 1 cycle 2 cycle 3 cycle 4 cycle 5
Figure 6. Yield of methyl lactate (ML) obtained with MIP-177-LT(Ti/Sn) using sucrose
(160 ºC for 24 h, 160 mg of catalyst and 225 mg of sugar). Error bars derived from 5
different experiments (cycle 1), 4 different experiments (cycle 2), 3 different experiments
(cycle 3), 2 different experiments (cycle 4) and 3 analyses from 1 experiment (cycle 5).
Table 2. Results of the analysis of titanium and tin by X-ray fluorescence (XRF) in
catalyst MIP-177-LT(Ti/Sn) before reaction and after 1, 3 and 5 cycles of reaction (see
Fig. 6). With the used catalyst from cycle 1, cycle 1b corresponds to a run in which no
sugar was added to the reactor.
15
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
BET surface
Pore volume
[cm3/g] a
Sample
[m2/g]
Ti (wt.%)
20±0.1
Sn (wt.%)
MIP-177-
LT(Ti/Sn)
Cycle 1
Cycle 1b
Cycle 2
Cycle 3
Cycle 4
Cycle 5
466±5
0.42
6.9±0.2
95±1
250±1
109±1
85±1
0.18
0.33
0.18
0.17
0.16
0.15
19±0.1
6.6±0.1
-
-
-
-
18±0.2
-
5.9±0.2
-
89±1
112±1
18±0.3
5.6±0.1
a At 0.96 of relative pressure.
3.
Conclusions
A new MOF (UZAR-S10) with the empirical formula of [(NH2-BDC)Sn]·(NH2-
BDC)0.5 was synthesized with the aim of improving the MOF performance in the
transformation of glucose and sucrose into methyl lactate. UZAR-S10 is a crystalline
material consisting of sheet like crystals of 3-5 m with ca. 300 nm thicknesses and
contains one structural ligand molecule and half ligand molecule trapped in the MOF
structure per Sn atom. The attempts to activate this material by solvent extraction with
methanol, DMF or sequences of both did not produce a satisfactory result, even though
the above mentioned half ligand molecule trapped in the MOF porosity suggested a high
porosity. The highest BET specific surface area value measured was 39 m2/g. In fact, the
removal of that half ligand molecule by either solvent extraction of thermal treatment
damaged the structure of UZAR-S10, making not possible its activation.
16
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
When compared in terms of glucose conversion to methyl lactate at the same
reaction conditions (160 ºC for 20 h using 160 mg of catalyst and 225 mg of sugar), the
methyl lactate yield of UZAR-S10 (10.2%) was better than those of the benchmark MOFs
MIL-53(Al), NH2-MIL-53(Al), HKUST-1 and MIL-101(Cr), similar to that UiO-66
(9.7%) and lower than that of ZIF-8 (19.8%). However, the methyl lactate yield achieved
with UZAR-S10 using sucrose instead of glucose was, at the best tested conditions (160
ºC for 48 h using 160 mg of catalyst and 225 mg of sugar), 29.5%, not far from the best
value of 34.8% reached in our previous work with ZIF-8. Finally, the highest value of
methyl lactate yield (42.0%) was obtained from sucrose with MIP-177-LT(Ti/Sn), a MOF
prepared by Sn metal exchange from the newly reported Ti tetracarboxylate MIP-177-
LT, that maintained a methyl lactate yield of 33.4% after five successive reaction runs.
These results confirm that the presence of Sn in the MOF is of paramount importance to
achieve a high yield to methyl lactate.
4.
Experimental
4.1. Synthesis of MOFs
A new method has been developed to synthesize a Sn-carboxylate MOF called
UZAR-S10 from SnCl2·2H2O and NH2-H2BDC (2-aminobenzene-1,4-dicarboxylic acid,
Sigma Aldrich, 99%). The precursor dispersion had a molar ratio of Sn2+:NH2-
H2BDC:H2O= 1:0.25:136. A typical synthesis of UZAR-S10 is as following. Firstly, 1.50
g of NH2-H2BDC (99 % purity, Sigma-Aldrich) was dissolved in 10 mL of deionized
water. Secondly, 1.84 g of SnCl2·2H2O (98 %, Sigma-Aldrich) was dissolved in 10 mL
of deionized water. Each solution was stirred individually for 5-10 min after which the
solution containing the metal precursor was added to the linker solution. The mixture was
17
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
transferred to a Teflon vessel (that of a 45 mL Teflon-lined stainless steel autoclave) and
outgassed at room temperature in an ultrasound bath for 15 min. The synthesis reaction
took place at 150 ºC for 5 h. The product obtained was recovered by centrifugation at
10000 rpm for 10 min, washed twice with deionized water by centrifugation under the
same conditions and dried at 100 ºC for 24 h. MIP-177-LT(Ti/Sn) was synthesized
following the directions given in.[25]
4.2. Catalytic reaction
The sugar conversion to methyl lactate was carried out in a batch reactor, a 35 mL
Teflon-lined stainless steel autoclave. Glucose (99 %, Alfa-Aesar) and sucrose (99 %,
Fluka) were chosen as representative carbohydrates due to their low cost, purity,
simplicity and abundance. The reaction was performed by dissolving 225 mg of
carbohydrate in 8.0 g of methanol (HPLC grade, Scharlau). Besides, 30 mg of
naphthalene (99 %, Sigma-Aldrich) was added as internal standard for subsequent
quantification of the yields. The amount of catalyst added was 160 mg. The mixture with
the sugar totally dissolved was transferred to a 45 mL Teflon-lined stainless steel
autoclave and the synthesis was carried out in an oven. The oven was heated with a ramp
of 1 h up to 160 ºC. The reaction time (24 h) starts when the reaction temperature is
reached under rotating conditions (15 r.p.m, i.e. the whole autoclave rotates
perpendicularly to its axial axis). These conditions used to transform the sugars in the
presence of solid catalysis were based on our previous reports.[15, 20]
Afterwards, the catalyst was recovered by centrifugation and the reaction liquid was
analyzed by gas chromatography with a mass detector (GC-MS). The equipment was an
Agilent 6850 GC system with a capillary column HP-5MS (30 m x 0.250 mm x 0.25 µm)
coupled with an Agilent 5975 MSD. The yields of the different products were calculated
18
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
using the internal standard method and calibration curves using commercial compounds:
methyl-S-(-)-lactate (98 %, Sigma-Aldrich), methylglyoxal 1,1-dimethylacetal (97 %,
Sigma-Aldrich), also called pyruvaldehyde dimethyl acetal, and 1,1,2,2–
tetramethoxypropane (99 %, Sigma-Aldrich).
The determination of sugars was carried out using a commercial analytical method
(Sucrose/Fructose/D-Glucose Assay Kit, Megazyme). The analysis was carried out as
follows: firstly, the sugar samples were mixed with a solution which contains enzymes
(different for each sugar), these enzymes transform sugars to glucose-6-phosphate (G-6-
P), and reaction lasts for a few minutes. Then another solution containing nicotinamide-
adenine dinucleotide phosphate (NADP+) and enzyme glucose-6-phosphate
dehydrogenase (G6P-DH) was added. In the presence of this enzyme, G-6-P is oxidized
by NADP+ producing its reduced form (NADPH), which is measured by increasing its
absorbance at 340 nm using a UV-Vis-NIR spectrophotometer Jasco V-670.
4.3. Catalyst characterization
The diffraction patterns of the samples were measured by powder X-ray diffraction
(PXRD) using a D-Max Rigaku X-ray diffractometer with Cu-Kα1 radiation (λ = 1.5418
Å) and a graphite monochromator. X-ray fluorescence (XRF) analyses (using a Thermo
Electron ARL ADVANT'XP equipped with a rhodium tube and UNIQUANT software)
were carried out on some selected samples. Thermodiffractometry was performed under
vacuum in a furnace coupled to a Siemens diffractometer with a copper anode and a
graphite monochromator to select the same Cu-Kα1 radiation. Each PXRD pattern was
recorded for 20 min in the 2.5-40° 2θ range with a 0.01º/s scanning rate at 25, 100, 150,
200, 275 and 300 °C with a heating rate of 10 ºC/min. Thermogravimetric analyses (TGA)
were carried out using Mettler Toledo TGA/SDTA 851e equipment. Samples were heated
19
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
in air up to 800 ºC with a heating rate of 10 ºC/min. Scanning electronic microscopy
(SEM) images were obtained over Pt-coated specimens using an Inspect F50 model
scanning electron microscope (FEI). Nitrogen adsorption-desorption isotherms were
obtained with a Micromeritics Tristar 3000. Previously, the samples were degassed at 200
ºC for 8 h under vacuum. Fourier transformed infrared spectra were measured on a Bruker
Vertex 70 FTIR with a deuterated triglycine sulfate (DTGS) detector and ATR Golden
Gate accessory in the range 600-1,800 cm-1, with an accuracy of 4 cm-1.
5.
Acknowledgments
Financial support from the Spanish Ministry of Economy and Competitiveness
(MAT2016-77290-R) and the European Social Fund (ESF) through the Aragón
Government (T43-17R) is gratefully acknowledged. The authors would like to
acknowledge the University of Zaragoza for the use of the Servicio General de Apoyo a
la Investigación-SAI and the Laboratorio de Microscopías Avanzadas (LMA) at INA.
6.
References
[1]
M. Dusselier, P. Van Wouwe, A. Dewaele, E. Makshina, B. F. Sels, Energ.
Environ. Sci. 2013, 6, 1415-1442.
[2]
F. A. Castillo Martinez, E. M. Balciunas, J. M. Salgado, J. M. Domínguez
González, A. Converti, R. P. d. S. Oliveira, Trends Food Sci. Tech. 2013, 30, 70-
83; R. Datta, M. Henry, J. Chem. Tech. Biotech. 2006, 81, 1119-1129.
S. Inkinen, M. Hakkarainen, A. C. Albertsson, A. Sodergard, Biomacromolecules
2011, 12, 523-532; A. P. Gupta, V. Kumar, Eur. Polym. J. 2007, 43, 4053-4074.
W. S. Chow, E. L. Teoh, J. Karger-Kocsis, Express Polym. Lett. 2018, 12, 396-
417.
[3]
[4]
20
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
[5]
R. P. John, A. G.S, K. M. Nampoothiri, A. Pandey, Biotech. Adv. 2009, 27, 145-
152.
[6]
[7]
Y. J. Wee, J. N. Kim, H. W. Ryu, Food Tech. Biotech. 2006, 44, 163-172.
L. Zhou, L. Wu, H. Li, X. Yang, Y. Su, T. Lu, J. Xu, J. Mol. Catal. A: Chem. 2014,
388-389, 74-80.
[8]
[9]
Y. Hayashi, Y. Sasaki, Chem. Commun. 2005, 2716-2718.
M. S. Holm, S. Saravanamurugan, E. Taarning, Science 2010, 328, 602-605.
[10] M. S. Holm, Y. J. Pagan-Torres, S. Saravanamurugan, A. Riisager, J. A. Dumesic,
E. Taarning, Green Chem. 2012, 14, 702-706.
[11] E. Taarning, S. Saravanamurugan, M. S. Holm, J. Xiong, R. M. West, C. H.
Christensen, ChemSusChem 2009, 2, 625-627.
[12] C. M. Osmundsen, M. S. Holm, S. Dahl, E. Taarning, Proc. Math. Phys. Eng. Sci.
2012, 468, 2000-2016.
[13] P. P. Pescarmona, K. P. F. Janssen, C. Delaet, C. Stroobants, K. Houthoofd, A.
Philippaerts, C. De Jonghe, J. S. Paul, P. A. Jacobs, B. F. Sels, Green Chem. 2010,
12, 1083-1089; R. M. West, M. S. Holm, S. Saravanamurugan, J. Xiong, Z.
Beversdorf, E. Taarning, C. H. Christensen, J. Catal. 2010, 269, 122-130.
[14] L. Li, X. Collard, A. Bertrand, B. F. Sels, P. P. Pescarmona, C. Aprile, J. Catal.
2014, 314, 56-65; L. Li, C. Stroobants, K. F. Lin, P. A. Jacobs, B. F. Sels, P. P.
Pescarmona, Green Chem. 2011, 13, 1175-1181.
[15] B. Murillo, A. Sanchez, V. Sebastian, C. Casado-Coterillo, O. de la Iglesia, M. P.
Lopez-Ram-de-Viu, C. Tellez, J. Coronas, J. Chem. Tech. Biotech. 2014, 89, 1344-
1350.
[16] J. Wang, Y. Masui, M. Onaka, Appl. Catal. B: Environ. 2011, 107, 135-139.
21
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
[17] A. Onda, T. Ochi, K. Kajiyoshi, K. Yanagisawa, Appl. Catal. A: Gen. 2008, 343,
49-54.
[18] G. Epane, J. C. Laguerre, A. Wadouachi, D. Marek, Green Chem. 2010, 12, 502-
506.
[19] F. de Clippel, M. Dusselier, R. Van Rompaey, P. Vanelderen, J. Dijkmans, E.
Makshina, L. Giebeler, S. Oswald, G. V. Baron, J. F. M. Denayer, P. P.
Pescarmona, P. A. Jacobs, B. F. Sels, J. Am. Chem. Soc. 2012, 134, 10089-10101.
[20] B. Murillo, B. Zornoza, O. de la Iglesia, C. Tellez, J. Coronas, J. Catal. 2016, 334,
60-67.
[21] A. Herbst, C. Janiak, CrystEngComm 2017, 19, 4092-4117.
[22] A. Clearfield, Dalton Trans. 2008, 6089-6102.
[23] X. Q. Wang, L. M. Liu, T. Makarenko, A. J. Jacobson, Cryst. Growth Des. 2010,
10, 3752-3756; A. C. Wibowo, M. D. Smith, H. C. zur Loye, Solid State Sci. 2011,
13, 607-615.
[24] M. H. Xie, X. L. Yang, C. Zou, C. D. Wu, Inorg. Chem. 2011, 50, 5318-5320.
[25] S. J. Wang, T. Kitao, N. Guillou, M. Wahiduzzaman, C. Martineau-Corcos, F.
Nouar, A. Tissot, L. Binet, N. Ramsahye, S. Devautour-Vinot, S. Kitagawa, S.
Seki, Y. Tsutsui, V. Briois, N. Steunou, G. Maurin, T. Uemura, C. Serre, Nat.
Commun. 2018, 9.
[26] S. Bourrelly, P. L. Llewellyn, C. Serre, F. Millange, T. Loiseau, G. Ferey, J. Am.
Chem. Soc. 2005, 127, 13519-13521.
[27] E. A. Alarcón, A. L. Villa, C. Montes de Correa, Microporous Mesoporous Mater.
2009, 122, 208-215.
[28] W. Dong, Z. Shen, B. Peng, M. Gu, X. Zhou, B. Xiang, Y. Zhang1, Sci. Rep. 2016,
26713.
22
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
[29] M. Dusselier, B. F. Sels, in Selective Catalysis for Renewable Feedstocks and
Chemicals, Vol. 353 (Ed.: K. M. Nicholas), Springer International Publishing,
2014, pp. 85-125.
[30] L. S. Yang, X. K. Yang, E. Tian, V. Vattipalli, W. Fan, H. F. Lin, J. Catal. 2016,
333, 207-216.
[31] F. Gandara, B. Gornez-Lor, E. Gutierrez-Puebla, M. Iglesias, M. A. Monge, D. M.
Proserpio, N. Snejko, Chem. Mater. 2008, 20, 72-76; R. Srirambalaji, S. Hong, R.
Natarajan, M. Yoon, R. Hota, Y. Kim, Y. H. Ko, K. Kim, Chem. Commun. 2012,
48, 11650-11652.
[32] A. Herbst, A. Khutia, C. Janiak, Inorg. Chem. 2014, 53, 7319-7333.
[33] A. Vimont, H. Leclerc, F. Mauge, M. Daturi, J. C. Lavalley, S. Surble, C. Serre,
G. Ferey, J. Phys. Chem. C 2007, 111, 383-388.
[34] K. S. Park, Z. Ni, A. P. Cote, J. Y. Choi, R. D. Huang, F. J. Uribe-Romo, H. K.
Chae, M. O'Keeffe, O. M. Yaghi, Proc. Natl. Acad. Sci. U S A 2006, 103, 10186-
10191.
[35] D. Fairen-Jimenez, S. A. Moggach, M. T. Wharmby, P. A. Wright, S. Parsons, T.
Duren, J. Am. Chem. Soc. 2011, 133, 8900-8902.
[36] N. Liedana, A. Galve, C. Rubio, C. Tellez, J. Coronas, ACS Appl. Mater. Interfaces
2012, 4, 5016-5021.
23
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900310
European Journal of Inorganic Chemistry
Table of Contents Entry
New MOF type material UZAR-S10 ([(NH2-BDC)Sn]·(NH2-BDC)0.5), i.e., and MOF
MIP-177-LT(Ti/Sn) applied to the production of methyl lactate from sugars.
Sn-carboxylate
MOF
24
This article is protected by copyright. All rights reserved.